Surface water - groundwater interactions in transition environments: the example of the Rio de la Plata coastal plain, Argentina

Environmental isotopes were successfully used to trace surface water-groundwater interactions in a multilayer aquifer system, and to propose a conceptual model for the hydrogeological systems of Rio de la Plata Coastal Plain. The objective of this work was to identify the surface water contribution to the recharge of the aquifers. A monitoring network of 50 wells for isotopic and geochemical analysis was established, covering different aquifers. According to the results a hydrogeological model has been proposed. The phreatic aquifer is directly recharged by the Rio de la Plata during level oscillations and indirectly during flooding events by feeding the marshes acting as recharge ponds. Artificial and natural channels act also as recharging lines. The recharge of the semi-confined aquifers occurs through lateral flow driven by the induced permanent landward gradients. River acts as a positive barrier, and beyond it, there is no possibility for the depression cones to expand. (author)